Blood haemoglobin (Hb) and related components were determined in a representative sample (n = 973, 449 men and 524 women) of a 70-year-old population, reinvestigated at age 75, 79 and 81. At age 81, 145 men and 259 women remained in the study. Longitudinal analysis demonstrated a significant decline in Hb concentration with advancing age, in the total study groups as well as in subsamples remaining after exclusions due to disease. The mean annual decline from age 70 to 81 in a subsample without definable disorders was in men 0.063 g/dl, in women 0.035 g/dl. There was a similar decline among subjects with high, intermediate or low Hb concentrations during the study. Only part of the observed intraindividual variations could be explained by factors other than age.